Commercial scale wind turbines are usually grouped together into wind turbine arrays, which are also referred to as a wind farms or wind parks. This enables the wind park operator to take advantage of economies of scale for installation and maintenance purposes, for example.
The nacelles of wind turbines are sometimes accessed by helicopter in order for maintenance to be carried out. This is particularly the case in offshore wind parks in which aerial access is much more cost-effective since maintenance personnel can be delivered to a specific wind turbine with suitable tools and components at a relatively low cost.
In order for maintenance personnel to be delivered to the correct wind turbine, it is of course necessary for wind turbines to be identifiable from the air. Therefore, it is known for the nacelles of wind turbines to be fitted with an ID plate which displays a suitable ID mark in large-enough characters so that it can be read at a distance by aircrew.
However, a drawback of this approach to marking a nacelle is that the ID plates are typically large and unwieldy items that are difficult to fit in the gusty conditions common to wind turbine sites, so it is usually preferable to fit them prior to installation. However, it may be the case that the individual wind turbines of a wind park are allocated identification numbers only after the wind turbines have been installed, for example during a commissioning exercise. It will be appreciated therefore, that it may not be practical to install ID plates on nacelles at this point. So a solution is required to enable identification numbers to be applied to wind turbines after commissioning but in a way that is practical in the extreme weather conditions usually encountered at nacelle-height.
It is against this background that the invention has been devised.